As is well known, to those skilled in the art, when sulfur-containing charge hydrocarbons are admitted to a fluid catalytic cracking (FCC) reactor, the charge is converted to lower boiling products including those falling within the motor fuel boiling range. A portion of the sulfur in the charge hydrocarbon is liberated in the reactor as hydrogen sulfide and mercaptans which may be separated from the FCCU cracked products. A portion of the sulfur is fixed on the coke-containing spent catalyst which is passed from the reaction zone to the regeneration zone wherein an oxygen-containing gas is provided to regenerate the spent catalyst. The gas so formed also includes oxides of sulfur (principally sulfur dioxide plus some sulfur trioxide); and thes oxides of sulfur may be the predominant undesirable species in the regenerator off-gas.
Economic considerations prevent the effective removal of sulfur oxides from the regenerator off gas; and environmental considerations dictate that they be decreased. Prior art attempts include operation under conditions such that the sulfur in the regeneration zone is fixed on the catalyst (thereby lowering the SO.sub.x content of the regenerator off-gas); and the sulfur is released as additional mercaptan and hydrogen sulfide in the reaction zone. Here these sulfur compositions may be readily passed to effluent separation operations which would not be the case for sulfur-containing gases recovered as regenerator waste-gas.
Illustrative of prior art endeavors in this area include those disclosed in U.S. Pat. No. 4,344,926 which issued Aug. 17, 1982 to Texaco Inc. as assignee of Randall H. Petty and Burton H. Bartley (the text of which is incorporated herein by reference) and the prior art cited therein.
A related application is Ser. No. 522,078, filed Aug. 11, 1983 entitled Control of SO.sub.x Emission by Lewis, Dai, and Holst.
It is an object of this invention to provide a process for removing a gaseous sulfur compound from a mixture of gases containing sulfur oxides. Other objects will be apparent to those skilled in the art.